Added command-line option support, help message.

[lelanthran]

1. Added support for setting each individual flag on the command-line.
2. Added a help message invoked with '--help'. Request for help overrides
   all other options.
3. Added command-line option --list-hashes to list supported hash
   algorithms. Request for list of hashes overrides all other options
   except --help.
4. By default the g_testAll flag was set; with command-line option
   '--test-all' this is no longer needed.
5. Basic sanity checking to ensure that at least one test is selected
   on the command-line.